164 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



peripheral ganglia, situated at various points along the viscera, some at 

 some distance from the sympathetic centres. 



In the sympathetic system four kinds of nervous elements are to be 

 distinguished. The original trunk that grows out (the ramus visceralis) 

 consists of motor and sensory fibres. The latter arise from ganglion 

 cells in the ganglia of the dorsal roots. The motor fibres have their 

 cell bodies in the cord at about the level of the lateral cornu, and pass 



somatic motor 



visceral sensory 



somatic sensory 

 sympathetic 



FIG. 166. Diagram of the relations of the sympathetic system, based on Huber. The 

 character of the different fibres is shown by conventional lines, bv, blood-vessel; eg, chain 

 ganglion; d, dorsal ramus; dr, dorsal root; g, gland; gr, gray ramus; pg, peripheral ganglion; 

 pvg, prevertebral ganglion; st, sympathetic trunk; v, ventral ramus; vi, visceral ramus; vr, 

 ventral root; wr, white ramus. 



out, in the lower vertebrates by the dorsal, in the mammals by the 

 ventral root. In the sympathetic system itself there are sensory and 

 motor (excitatory) cells, derived from the ganglion cells carried down 

 by the growing nerves. These develop their dendrites and axons, 

 and some of these run up the rami communicantes to the dorsal and 

 ventral rami, and follow along them to the peripheral glands and 

 blood-vessels of the body. Others grow into the various viscera. These 

 purely sympathetic fibers are not medullated and hence are gray in 



